Safety switch for an industrial machine

ABSTRACT

The invention relates to a safety switch intended to be connected into a safety circuit for an industrial machine, for example an industrial robot. The switch comprises a contact device (2) with a hand-operated device (3, 4) in which a pressure rod (31) is displaceable against the action of a return spring (33) from a first end position via an operating position to a second end position, the safety circuit being closed only in the operating position. During the return movement of the pressure rod from its second to its first end position, the contact device (2) is not affected, and the safety circuit thus remains open during the whole of this return movement.

TECHNICAL FIELD

The present invention relates to a hand-operated safety switch for anindustrial machine, intended to be connected with an emergency stopcircuit for the machine. The safety switch is primarily intended to beused in applications in the engineering industry, for example in anindustrial robot application where persons are present within theoperating range of the robot.

BACKGROUND ART

An industrial robot can be controlled with the aid of a joystick. Duringa teaching or programming procedure, the position and/or orientation ofthe robot tool can be controlled in the desired manner by means of thejoystick. The joystick can either be arranged on a fixed control cabinetor on a smaller, separate programming unit, which during programming orteaching can be held in the hand or be placed on a table. In order thatprogramming shall not take an unreasonably long time, it is necessarythat a full deflection of the joystick causes a movement with arelatively high speed of response in the robot. During the teachingprocedure it may be necessary for personnel to stay in the vicinity ofthe robot in order to eliminate the risks of injuries which arise inthis connection, a safety plate is arranged on programming units of theabove-mentioned kind, on which safety plate the operator's hand restswhen operating the joystick with the aid of the fingers. When the handis removed, the safety plate senses this and influences the controlsystem such that the joystick is rendered inoperative. In this way, itis prevented that an unintentional contact with the joystick gives riseto a movement of the robot. A device of this kind is described inSwedish printed patent application 450 285 and in Asea Journal 1982, No.6, pp. 145-150.

In the known device there may be a certain risk that the operator, in anemergency situation, reacts incorrectly and instead of removing his handfrom the safety plate presses even harder, whereby the robot continuesits movement with an ensuing risk of both material damage and personalinjury. To avoid this it has been proposed to use a contact device,actuated by the safety device, with two end positions located ondifferent sides of an operating position, one of the end positionsconstituting the initial position (the rest position) and the other endposition an extra neutral position. A drawback with this design,however, is that the contact device while returning to the initialposition has to pass the operating position, whereby the safety circuitis briefly closed with an ensuing risk of uncontrolled movements of therobot.

SUMMARY OF THE INVENTION

The present invention aims to provide a safety switch designed for theabove-mentioned field of use, which does not suffer from theabove-mentioned drawbacks of comparable prior art designs. This isachieved according to the invention by a safety switch with thecharacteristic features stated in the claims.

The safety switch according to the invention comprises a contact devicewith a hand-operated device in which a pressure operating member isdisplaceable against the action of a return spring from a first endposition via an operating position to a seconded end position, wherebythe safety circuit, into which the switch is intended to be connected,is connected only in the operating position. The operating device isarranged such that the contact device is not affected during the returnmovement of the pressure operating device from its second to its firstend position, and thus the safety circuit remains open during the wholeof this return movement.

A safety switch according to the invention makes it possible forindustrial machines of the above-mentioned kind to be installed, usedand maintained with an adequate degree of safety against personalinjury. In addition, the switch is simple to manufacture and mount.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in greater detail by describing anembodiment with reference to the accompanying drawings, wherein

FIG. 1 is a side view of a safety switch according to the invention inits initial position (first end position),

FIG. 2 shows the switch in the same position in a view from above,

FIGS. 3 and 4 are side views of the switch in its operating position(mid-position) and in its second end position, respectively,

FIGS. 5, 6 and 7 show the housing of the switch in a view from the side(FIG. 5), in an end view from the left (FIG. 6), and in a view fromabove (FIG. 7), respectively,

FIGS. 8 and 9 show a pressure rod, included in the operating member ofthe switch, in a side view and in an end view from the left,respectively, and

FIGS. 10 and 11 show a lever arm, included in the switch, in a side viewand a view from the left, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The safety switch shown in FIG. 1 comprises a housing 1, in the upperpart of which a microswitch 2 is fixed and in the lower part of which anoperating member 3 in the form of a pressure rod 31 with a pressureplate 32 is journalled so as to be longitudinally displaceable. Betweenthe pressure plate 32 and the housing 1, a compression spring (returnspring) 33 is arranged.

The microswitch 2 comprises at least one contact pair with one fixed andone movable contact 21 and 22, respectively. With the aid of anactuating member 23, the movable contact 22 may be displaced from theopen position shown in FIG. 1 to the closed position shown in FIG. 3.The movable contact is permanently influenced by a return spring 24 in adirection towards the open position.

The transmission of the operating force from the operating member 3 tothe microswitch 2 is achieved by a lever arm 4 which, with the aid of acylindrical pin 41, is rotatably journalled in the housing 1. In thelower part of the lever arm 4 there are a compression spring 42 and aball 43. The spring-loaded ball 43 presses against the pressure rod 31,which is provided with a recess 36 (FIG. 4), arranged at that end of therod which is located furthest away from the pressure plate 32 andcooperating with the ball 43, for achieving a coupling engagementbetween the pressure rod and the lever arm. The upper end portion of thelever arm makes contact with the actuating member 23 of the microswitch.

As is clear from FIGS. 5-7, the housing 1 of the safety switch isprovided, in its upper part, with a fixing hole 11 for the microswitch 2and, in its lower part, with a bearing hole 12 with guide slots 13 forthe pressure rod 31. The center lines of the holes 11, 12 are parallel.Between the orifices of the holes 11, 12 on one side of the housing 1,two parallel wall portions 14, 15 extend, between which the lever arm 4is intended to be mounted. The wall portions are provided withthrough-holes 16 for the bearing pin 41 of the lever arm. Further, thehousing 1 is provided with two fixing holes 17 for fixing the safetyswitch in, for example, a programming box for an industrial robot.

The pressure rod 31, which is shown separately in FIGS. 8 and 9, has asubstantially circular cross section and is provided at one end with anaxial hole 34 for fixing the pressure plate 32. At its other end thepressure rod is provided with a recess which, nearest the end surface ofthe rod, is made with a deeper portion 36 which forms a seat for theball 43 and which, via a shoulder 37, changes into a shallower portion38 which forms a rolling or sliding path for the ball 43. The height ofthe shoulder is considerably smaller than the diameter of the ball, forexample about 1 mm if the diameter of the ball is 4 mm. The shoulder cansuitably be made inclined so as to obtain a more even transition betweenthe two portions 36 and 38. In the embodiment shown the shoulder 37forms an angle of about 45° with the longitudinal axis of the pressurerod.

The pressure rod 31 is provided with radially projecting guide pins 39which fit into the guide slot 13 of the housing. The pins 39 limit theaxial movement of the pressure rod in a direction towards the right tothe end position shown in FIG. 1 and also prevents the rod from movingin the direction of rotation.

The lever arm 4 is shown separately in FIGS. 10 and 11. It has atransversal hole 44 for the bearing pin 41 as well as a longitudinalhole 45 for accomodating the compression spring 42 and the ball 43. Thecentre lines of the holes 44, 45 are directed perpendicularly to eachother. At the orifice of the hole 45, there is a transversal hole 46 fortemporary insertion of a mounting pin to keep the compression spring 42and the ball 43 fixed in the hole 45 during mounting.

The pressure rod 31 is suitably made of a plastic material, for exampleacetal plastic, whereas the other parts, such as the housing 1 and thelever arm 4, are suitably made of metal.

The safety switch operates as follows: In the initial position shown inFIG. 1, the spring 33 keeps the pressure rod 31 in its first endposition, and the spring 24 built into the microswitch keeps the switchin the open position, whereby the safety loop into which the switch isconnected is open. By pressing on the pressure plate 32, the pressurerod 31 is pressed in and influences the lever arm 4 which, in its turn,presses the actuating member 23 of the microswitch into the operatingposition shown in FIG. 3, in which the safety loop is closed. In normaloperation, the movement on the pressure rod takes place between theinitial position according to FIG. 1 and the operating positionaccording to FIG. 3.

When in the operating position according to FIG. 3 and an emergencysituation arises, the pressure plate can either be released or bepressed in further. In the latter case, an increased pressure isrequired for the ball 43 to pass the shoulder 37 between the deeperportion 36 and the shallower portion 38 on the pressure rod. Thisincreased pressure is determined by the spring 42. When the ball hasarrived on the shallower portion 38 of the pressure rod, the lever arm 4is disengaged from the pressure rod and the microswitch can return toits open position while being influenced by the return spring 24, whilecontinuing the pressing of the pressure rod until the rod has reachedits second end position according to FIG. 4. Also in this end position,the safety loop is thus open.. To get from the second end positionaccording to FIG. 4 to the first end position (initial position)according to FIG. 1, the pressure plate 32 is released and the switchresumes the initial position with the aid of the spring 33. During thereturn movement of the pressure rod from the second to the first endposition, the microswitch 2 is not influenced, and the safety loop isthus open during the whole return movement.

A considerable advantage with the described switch design is that noadjustment is required when mounting the switch.

The invention is not limited to the embodiment shown but severalmodifications are possible within the scope of the claims.

I claim:
 1. A safety switch for an industrial machine, said switchcomprisinga housing, a contact device mounted in said housing and beingswitchable between an open position and a closed position, said contactdevice comprising a spring for biasing the contact device in a directiontoward said open position, a hand-operated device for switching saidcontact device between said open position and said closed position, saidhand-operated device comprising a pressure operating member and a leverarm for transmitting operating force from the pressure operating memberto the contact device, said lever arm being rotatably journalled in saidhousing and making contact at one of its end portions with the pressureoperating member through resilient means and at its other end portionwith an actuating member associated with the contact device, saidresilient means comprising a ball and a compression spring for pressingthe ball against a side surface of the pressure operating member, saidpressure operating member being displaceable against the action of areturn spring from a first end position via a mid-position to a secondend position, the pressure operating member being connected to thecontact device through said lever arm in such a way that the contactdevice assumes the open position when the operating member is in its endpositions and the closed position when the operating member is in itsmid-position, and that the contact device is not influenced by theoperating member when the, operating member returns from its second toits first end position.
 2. A safety switch according to claim 1, whereinthe pressure operating member comprises a pressure rod which islongitudinally displaceable in a bearing hole located in the housing,the rod being provided with transversely projecting guide pins which arein engagement with guide slots located in the housing, for limiting thereturn movement of the rod and for fixing the rod in the direction ofrotation.
 3. A safety switch according to claim 1, wherein the contactdevice comprises a microswitch.
 4. A safety switch according to claim 1wherein the side surface of the pressure operating member has a recesswhich is adapted such that, together with the resilient means of thelever arm, effects a coupling engagement between the operating memberand the lever arm during the displacement of the operating member fromits first end position to its mid-position, but which, during continueddisplacement of the operating member (31) from the mid-position towardsthe second end position, permits the ball to be pressed out of therecess, whereby the lever arm is disengaged from the operating member.5. A safety switch according to claim 4, wherein the recess in thepressure operating member has a deeper portion provided at one end ofthe pressure rod and forming a seat for the ball ,and the recess havinga shallower portion which forms a rolling or sliding path for the ball.